U.S. patent number 8,379,372 [Application Number 13/081,982] was granted by the patent office on 2013-02-19 for housing configuration for a solid electrolytic capacitor.
This patent grant is currently assigned to AVX Corporation. The grantee listed for this patent is Martin Biler, Jan Petrzilek, Stanislav Zednicek, Ivana Zednickova. Invention is credited to Martin Biler, Jan Petrzilek, Stanislav Zednicek, Ivana Zednickova.
United States Patent |
8,379,372 |
Zednicek , et al. |
February 19, 2013 |
Housing configuration for a solid electrolytic capacitor
Abstract
A capacitor assembly that is stable under extreme conditions is
provided. More particularly, the assembly includes a capacitor
element that is positioned within an interior cavity of a housing.
The housing includes a base to which the capacitor element is
connected. The housing also includes a lid that contains an outer
wall from which extends a sidewall. An end of the sidewall is
defined by a lip extending at an angle relative to the longitudinal
direction and having a peripheral edge located beyond a periphery
of the sidewall. The lip is hermetically sealed to the base. In
some cases, the peripheral edge of the lip is also coplanar with an
edge of the base. The use of such a lip can enable a more stable
connection between the components and improve the seal and
mechanical stability of the capacitor assembly, thereby allowing it
to better function under extreme conditions.
Inventors: |
Zednicek; Stanislav (Lanskroun,
CZ), Biler; Martin (Novy Jicin, CZ),
Petrzilek; Jan (Usti nad Orlici, CZ), Zednickova;
Ivana (Lanskroun, CZ) |
Applicant: |
Name |
City |
State |
Country |
Type |
Zednicek; Stanislav
Biler; Martin
Petrzilek; Jan
Zednickova; Ivana |
Lanskroun
Novy Jicin
Usti nad Orlici
Lanskroun |
N/A
N/A
N/A
N/A |
CZ
CZ
CZ
CZ |
|
|
Assignee: |
AVX Corporation (Fountain Inn,
SC)
|
Family
ID: |
46026377 |
Appl.
No.: |
13/081,982 |
Filed: |
April 7, 2011 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20120257328 A1 |
Oct 11, 2012 |
|
Current U.S.
Class: |
361/536; 361/525;
361/528; 361/535; 361/537; 361/523 |
Current CPC
Class: |
H01G
9/012 (20130101); H01G 9/10 (20130101); H01G
9/06 (20130101); H01G 9/08 (20130101); H01G
9/15 (20130101) |
Current International
Class: |
H01G
4/228 (20060101) |
Field of
Search: |
;361/536,516-517,523-525,528-529,535,537,540-541 |
References Cited
[Referenced By]
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WO 2009 043648 |
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WO |
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WO 2010 102751 |
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Sep 2010 |
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WO |
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Other References
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by applicant .
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by applicant .
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Resistant/Sealant, Mar. 2, 2011, 8 pages. cited by applicant .
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Conductive Polymer Technologies Based on
Poly(3,4-Ethylenedioxythiophene)," 2005 AIMCAL Fall Technical
Conference and 19.sup.th International Vacuum Web Coating
Conference, Oct. 16-20, 2005, Session 5: Advances in Technology,
Myrtle Beach, SC, 10 pages. cited by applicant .
Paper--Merker et al., "Conducting Polymer Dispersions for
High-Capacitance Tantalum Capacitors,": CARTS Europe 2006, Sep.
2006, Bad Homburg, Germany, 6 pages. cited by applicant .
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Tantalum Capacitors with Poly(3,4-Ethylenedioxythiophene) Cathode,"
Journal of the Electrochemical Society, vol. 156, No. 6, 2009, 10
pages. cited by applicant .
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Electrolytic Capacitors," CARTS Europe 2005, Oct. 17-20, 2005,
Prague, CZ Republic, 6 pages. cited by applicant .
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High-CV Tantalum Capacitors," CARTS Europe Oct. 29-Nov. 1, 2007,
Barcelona, Spain, 6 pages. cited by applicant .
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Capacitors," CMSE Europe 2010. cited by applicant .
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3 pages. cited by applicant .
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cited by applicant .
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2005) 17 pages. cited by applicant.
|
Primary Examiner: Ha; Nguyen T
Attorney, Agent or Firm: Dority & Manning, P.A.
Claims
What is claimed is:
1. A capacitor assembly comprising: a housing comprising a base
extending in a lateral direction and a lid that overlies the base
to define an interior cavity therebetween, wherein the lid contains
an outer wall and a sidewall extending in a longitudinal direction
from the outer wall toward the base, wherein a lip extends from the
sidewall at an angle relative to the longitudinal direction and is
hermetically sealed to the base, the lip having a peripheral edge
located beyond a periphery of the sidewall; a capacitor element
that is positioned within the interior cavity and connected to the
base of the housing, the capacitor element comprising an anode
formed from an anodically oxidized, sintered porous body and a
solid electrolyte overlying the anode; an anode termination that is
in electrical connection with the anode body; and a cathode
termination that is in electrical connection with the solid
electrolyte.
2. The capacitor assembly of claim 1, wherein the outer wall
defines a distal end of the lid and the lip defines a proximal end
of the lid.
3. The capacitor assembly of claim 1, wherein the peripheral edge
of the lip is generally coplanar with a peripheral edge of the
base.
4. The capacitor assembly of claim 1, wherein the peripheral edge
of the lip extends in a direction that is generally perpendicular
to the lateral direction of the base.
5. The capacitor assembly of claim 1, wherein the sidewall extends
in a direction that is generally perpendicular to the lateral
direction of the base.
6. The capacitor assembly of claim 1, wherein the lip extends from
the sidewall in a direction that is generally parallel to the
lateral direction of the base.
7. The capacitor assembly of claim 1, wherein the angle between the
sidewall and the lip is from about 80.degree. to about
100.degree..
8. The capacitor assembly of claim 1, wherein a sealing member is
disposed between the lip and the base.
9. The capacitor assembly of claim 1, wherein opposing sidewalls
extend from the outer wall of the lid in a longitudinal direction
toward the base, wherein a lip extends from each of the sidewalls
at an angle relative to the longitudinal direction and is
hermetically sealed to the base, each lip having a peripheral edge
located beyond a periphery of a sidewall.
10. The capacitor assembly of claim 1, wherein the interior cavity
has a gaseous atmosphere that contains an inert gas.
11. The capacitor assembly of claim 10, wherein the capacitor
element occupies about 30 vol. % or more of the interior
cavity.
12. The capacitor assembly of claim 10, wherein inert gases
constitute from about 50 wt. % to 100 wt. % of the gaseous
atmosphere.
13. The capacitor assembly of claim 1, wherein the porous body is
formed from tantalum or niobium oxide.
14. The capacitor assembly of claim 1, wherein the solid
electrolyte includes a conductive polymer.
15. The capacitor assembly of claim 14, wherein the conductive
polymer is in the form of a particle dispersion.
16. The capacitor assembly of claim 1, wherein the base and the lid
are formed from a metal, plastic, ceramic, or a combination
thereof.
17. The capacitor assembly of claim 16, wherein the lid is formed
from a metal.
18. The capacitor assembly of claim 1, further comprising a lead
that extends in a lateral direction from the porous body of the
anode, wherein the lead is positioned within the interior cavity of
the housing.
19. The capacitor assembly of claim 18, further comprising a
connective member that contains a first portion that is positioned
generally perpendicular to the lateral direction of the anode lead
and connected thereto.
20. The capacitor assembly of claim 19, wherein the connective
member further contains a second portion that is generally parallel
to the lateral direction in which the anode lead extends.
21. The capacitor assembly of claim 20, wherein the second portion
is positioned within the housing.
Description
BACKGROUND OF THE INVENTION
Electrolytic capacitors (e.g., tantalum capacitors) are
increasingly being used in the design of circuits due to their
volumetric efficiency, reliability, and process compatibility. For
example, one type of capacitor that has been developed is a solid
electrolytic capacitor that includes an anode (e.g., tantalum), a
dielectric oxide film (e.g., tantalum pentoxide, Ta.sub.2O.sub.5)
formed on the anode, a solid electrolyte layer, and a cathode. The
solid electrolyte layer may be formed from a conductive polymer,
such as described in U.S. Pat. Nos. 5,457,862 to Sakata, et al.,
5,473,503 to Sakata, et al., 5,729,428 to Sakata, et al., and
5,812,367 to Kudoh, et al. Unfortunately, however, the stability of
such solid electrolytes is poor at high temperatures due to the
tendency to transform from a doped to an un-doped state, or vice
versa. In response to these and other problems, capacitors have
been developed that are hermetically sealed to limit the contact of
oxygen with the conductive polymer during use. U.S. Patent
Publication No. 2009/0244812 to Rawal, et al., for instance,
describes a capacitor assembly that includes a conductive polymer
capacitor that is enclosed and hermetically sealed within a ceramic
housing in the presence of an inert gas. The housing includes a lid
that is welded to the sidewalls of a base structure. According to
Rawal, et al., the ceramic housing limits the amount of oxygen and
moisture supplied to the conductive polymer so that it is less
likely to oxidize in high temperature environments, thus increasing
the thermal stability of the capacitor assembly. Despite the
benefits achieved, however, issues nevertheless remain. For
example, the welding of the lid to the sidewalls can be problematic
and lead to an imperfect seal where a small amount of moisture
and/or oxygen can enter. While this is not a problem in all
circumstances, it can become particularly troublesome under extreme
conditions of high temperature (e.g., above about 175.degree. C.)
and high voltage (e.g., above about 35 volts).
As such, a need currently exists for a housing configuration that
is capable of exhibiting improved hermetic sealing.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present invention, a
capacitor assembly is disclosed that comprises a housing. The
housing comprises a base extending in a lateral direction and a lid
that overlies the base to define an interior cavity therebetween.
The lid contains an outer wall and a sidewall extending in a
longitudinal direction from the outer wall toward the base. A lip
extends from the sidewall at an angle relative to the longitudinal
direction and is hermetically sealed to the base. The lip has a
peripheral edge located beyond a periphery of the sidewall. A
capacitor element is positioned within the interior cavity and
connected to the base of the housing. The capacitor element
comprises an anode formed from an anodically oxidized, sintered
porous body and a solid electrolyte overlying the anode. The
assembly also comprises an anode termination that is in electrical
connection with the anode body and a cathode termination that is in
electrical connection with the solid electrolyte.
Other features and aspects of the present invention are set forth
in greater detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
A full and enabling disclosure of the present invention, including
the best mode thereof, directed to one of ordinary skill in the
art, is set forth more particularly in the remainder of the
specification, which makes reference to the appended figures in
which:
FIG. 1 is a cross-sectional view of one embodiment of a capacitor
assembly of the assembly of the present invention;
FIG. 2 is an exploded cross-sectional view of the lid sidewall of
FIG. 1;
FIG. 3 is a cross-sectional view of yet another embodiment of a
capacitor assembly of the assembly of the present invention.
Repeat use of references characters in the present specification
and drawings is intended to represent same or analogous features or
elements of the invention.
DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS
It is to be understood by one of ordinary skill in the art that the
present discussion is a description of exemplary embodiments only,
and is not intended as limiting the broader aspects of the present
invention, which broader aspects are embodied in the exemplary
construction.
Generally speaking, the present invention is directed to a
capacitor assembly that is stable under extreme conditions. More
particularly, the assembly includes a capacitor element that is
positioned within an interior cavity of a housing. The housing
includes a base to which the capacitor element is connected. The
housing also includes a lid that contains an outer wall from which
extends a sidewall. A lip extends from the sidewall that is
hermetically sealed to the base. The lip has a peripheral edge
located beyond a periphery of the sidewall. In some cases, the
peripheral edge of the lip is also coplanar with an edge of the
base. The use of such a lip can enable a more stable connection
between the components and improve the seal and mechanical
stability of the capacitor assembly, thereby allowing it to better
function under extreme conditions.
Various embodiments of the present invention will now be described
in more detail.
I. Capacitor Element
For high voltage applications, it is often desired that the anode
of the capacitor element is formed from a powder having a
relatively low specific charge, such as less than about 70,000
microFarads*Volts per gram (".mu.F*V/g"), in some embodiments about
2,000 .mu.F*V/g to about 65,000 .mu.F*V/g, and in some embodiments,
from about 5,000 to about 50,000 .mu.F*V/g. Of course, although
powders of a low specific charge may sometimes be desired, it is by
no means a requirement. Namely, the powder may also have a
relatively high specific charge of about 70,000 microFarads*Volts
per gram (".mu.F*V/g") or more, in some embodiments about 80,000
.mu.F*V/g or more, in some embodiments about 90,000 .mu.F*V/g or
more, in some embodiments about 100,000 .mu.F*V/g or more, and in
some embodiments, from about 120,000 to about 250,000
.mu.F*V/g.
The powder may contain a valve metal (i.e., metal that is capable
of oxidation) or valve metal-based compound, such as tantalum,
niobium, aluminum, hafnium, titanium, alloys thereof, oxides
thereof, nitrides thereof, and so forth. For example, the valve
metal composition may contain an electrically conductive oxide of
niobium, such as niobium oxide having an atomic ratio of niobium to
oxygen of 1:1.0.+-.1.0, in some embodiments 1:1.0.+-.0.3, in some
embodiments 1:1.0.+-.0.1, and in some embodiments, 1:1.0.+-.0.05.
For example, the niobium oxide may be NbO.sub.0.7, NbO.sub.1.0,
NbO.sub.1.1, and NbO.sub.2. Examples of such valve metal oxides are
described in U.S. Pat. Nos. 6,322,912 to Fife; 6,391,275 to Fife et
al.; 6,416,730 to Fife et al.; 6,527,937 to Fife; 6,576,099 to
Kimmel, et al.; 6,592,740 to Fife, et al.; and 6,639,787 to Kimmel,
et al.; and 7,220,397 to Kimmel, et al., as well as U.S. Patent
Application Publication Nos. 2005/0019581 to Schnitter;
2005/0103638 to Schnitter, et al.; 2005/0013765 to Thomas, et al.,
all of which are incorporated herein in their entirety by reference
thereto for all purposes.
The particles of the powder may be flaked, angular, nodular, and
mixtures or variations thereof. The particles also typically have a
screen size distribution of at least about 60 mesh, in some
embodiments from about 60 to about 325 mesh, and in some
embodiments, from about 100 to about 200 mesh. Further, the
specific surface area is from about 0.1 to about 10.0 m.sup.2/g, in
some embodiments from about 0.5 to about 5.0 m.sup.2/g, and in some
embodiments, from about 1.0 to about 2.0 m.sup.2/g. The term
"specific surface area" refers to the surface area determined by
the physical gas adsorption (B.E.T.) method of Bruanauer, Emmet,
and Teller, Journal of American Chemical Society, Vol. 60, 1938, p.
309, with nitrogen as the adsorption gas. Likewise, the bulk (or
Scott) density is typically from about 0.1 to about 5.0 g/cm.sup.3,
in some embodiments from about 0.2 to about 4.0 g/cm.sup.3, and in
some embodiments, from about 0.5 to about 3.0 g/cm.sup.3.
Other components may be added to the powder to facilitate the
construction of the anode body. For example, a binder and/or
lubricant may be employed to ensure that the particles adequately
adhere to each other when pressed to form the anode body. Suitable
binders may include camphor, stearic and other soapy fatty acids,
Carbowax (Union Carbide), Glyptal (General Electric), polyvinyl
alcohols, naphthalene, vegetable wax, and microwaxes (purified
paraffins). The binder may be dissolved and dispersed in a solvent.
Exemplary solvents may include water, alcohols, and so forth. When
utilized, the percentage of binders and/or lubricants may vary from
about 0.1% to about 8% by weight of the total mass. It should be
understood, however, that binders and lubricants are not required
in the present invention.
The resulting powder may be compacted using any conventional powder
press mold. For example, the press mold may be a single station
compaction press using a die and one or multiple punches.
Alternatively, anvil-type compaction press molds may be used that
use only a die and single lower punch. Single station compaction
press molds are available in several basic types, such as cam,
toggle/knuckle and eccentric/crank presses with varying
capabilities, such as single action, double action, floating die,
movable platen, opposed ram, screw, impact, hot pressing, coining
or sizing. After compaction, the resulting anode body may then be
diced into any desired shape, such as square, rectangle, circle,
oval, triangle, hexagon, octagon, heptagon, pentagon, etc. The
anode body may also have a "fluted" shape in that it contains one
or more furrows, grooves, depressions, or indentations to increase
the surface to volume ratio to minimize ESR and extend the
frequency response of the capacitance. The anode body may then be
subjected to a heating step in which most, if not all, of any
binder/lubricant are removed. For example, the anode body is
typically heated by an oven that operates at a temperature of from
about 150.degree. C. to about 500.degree. C. Alternatively, the
binder/lubricant may also be removed by contacting the pellet with
an aqueous solution, such as described in U.S. Pat. No. 6,197,252
to Bishop, et al.
Once formed, the anode body is then sintered. The temperature,
atmosphere, and time of the sintering may depend on a variety of
factors, such as the type of anode, the size of the anode, etc.
Typically, sintering occurs at a temperature of from about from
about 800.degree. C. to about 1900.degree. C., in some embodiments
from about 1000.degree. C. to about 1500.degree. C., and in some
embodiments, from about 1100.degree. C. to about 1400.degree. C.,
for a time of from about 5 minutes to about 100 minutes, and in
some embodiments, from about 30 minutes to about 60 minutes. If
desired, sintering may occur in an atmosphere that limits the
transfer of oxygen atoms to the anode. For example, sintering may
occur in a reducing atmosphere, such as in a vacuum, inert gas,
hydrogen, etc. The reducing atmosphere may be at a pressure of from
about 10 Torr to about 2000 Torr, in some embodiments from about
100 Torr to about 1000 Torr, and in some embodiments, from about
100 Torr to about 930 Torr. Mixtures of hydrogen and other gases
(e.g., argon or nitrogen) may also be employed.
An anode lead may also be connected to the anode body that extends
in a lateral direction therefrom. The anode lead may be in the form
of a wire, sheet, etc., and may be formed from a valve metal
compound, such as tantalum, niobium, niobium oxide, etc. Connection
of the lead may be accomplished using known techniques, such as by
welding the lead to the body or embedding it within the anode body
during formation (e.g., prior to compaction and/or sintering).
The anode is also coated with a dielectric. The dielectric may be
formed by anodically oxidizing ("anodizing") the sintered anode so
that a dielectric layer is formed over and/or within the anode. For
example, a tantalum (Ta) anode may be anodized to tantalum
pentoxide (Ta.sub.2O.sub.5). Typically, anodization is performed by
initially applying a solution to the anode, such as by dipping
anode into the electrolyte. A solvent is generally employed, such
as water (e.g., deionized water). To enhance ionic conductivity, a
compound may be employed that is capable of dissociating in the
solvent to form ions. Examples of such compounds include, for
instance, acids, such as described below with respect to the
electrolyte. For example, an acid (e.g., phosphoric acid) may
constitute from about 0.01 wt. % to about 5 wt. %, in some
embodiments from about 0.05 wt. % to about 0.8 wt. %, and in some
embodiments, from about 0.1 wt. % to about 0.5 wt. % of the
anodizing solution. If desired, blends of acids may also be
employed.
A current is passed through the anodizing solution to form the
dielectric layer. The value of the formation voltage manages the
thickness of the dielectric layer. For example, the power supply
may be initially set up at a galvanostatic mode until the required
voltage is reached. Thereafter, the power supply may be switched to
a potentiostatic mode to ensure that the desired dielectric
thickness is formed over the entire surface of the anode. Of
course, other known methods may also be employed, such as pulse or
step potentiostatic methods. The voltage at which anodic oxidation
occurs typically ranges from about 4 to about 250 V, and in some
embodiments, from about 9 to about 200 V, and in some embodiments,
from about 20 to about 150 V. During oxidation, the anodizing
solution can be kept at an elevated temperature, such as about
30.degree. C. or more, in some embodiments from about 40.degree. C.
to about 200.degree. C., and in some embodiments, from about
50.degree. C. to about 100.degree. C. Anodic oxidation can also be
done at ambient temperature or lower. The resulting dielectric
layer may be formed on a surface of the anode and within its
pores.
The capacitor element also contains a solid electrolyte that
functions as the cathode for the capacitor. A manganese dioxide
solid electrolyte may, for instance, be formed by the pyrolytic
decomposition of manganous nitrate (Mn(NO.sub.3).sub.2). Such
techniques are described, for instance, in U.S. Pat. No. 4,945,452
to Sturmer, et al., which is incorporated herein in its entirety by
reference thereto for all purposes.
Alternatively, the solid electrolyte may be formed from one or more
conductive polymer layers. The conductive polymer(s) employed in
such layers are typically 7-conjugated and have electrical
conductivity after oxidation or reduction, such as an electrical
conductivity of at least about 1 .mu.S cm.sup.-1 after oxidation.
Examples of such .pi.-conjugated conductive polymers include, for
instance, polyheterocycles (e.g., polypyrroles, polythiophenes,
polyanilines, etc.), polyacetylenes, poly-p-phenylenes,
polyphenolates, and so forth. Particularly suitable conductive
polymers are substituted polythiophenes having the following
general structure:
##STR00001##
wherein,
T is O or S;
D is an optionally substituted C.sub.1 to C.sub.5 alkylene radical
(e.g., methylene, ethylene, n-propylene, n-butylene, n-pentylene,
etc.);
R.sub.7 is a linear or branched, optionally substituted C.sub.1 to
C.sub.18 alkyl radical (e.g., methyl, ethyl, n- or iso-propyl, n-,
iso-, sec- or tert-butyl, n-pentyl, 1-methylbutyl, 2-methylbutyl,
3-methylbutyl, 1-ethylpropyl, 1,1-dimethylpropyl,
1,2-dimethylpropyl, 2,2-dimethylpropyl, n-hexyl, n-heptyl, n-octyl,
2-ethylhexyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl,
n-tetradecyl, n-hexadecyl, n-octadecyl, etc.); optionally
substituted C.sub.5 to C.sub.12 cycloalkyl radical (e.g.,
cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl
cyclodecyl, etc.); optionally substituted C.sub.6 to C.sub.14 aryl
radical (e.g., phenyl, naphthyl, etc.); optionally substituted
C.sub.7 to C.sub.18 aralkyl radical (e.g., benzyl, o-, m-, p-tolyl,
2,3-, 2,4-, 2,5-, 2-6, 3-4-, 3,5-xylyl, mesityl, etc.); optionally
substituted C.sub.1 to C.sub.4 hydroxyalkyl radical, or hydroxyl
radical; and
q is an integer from 0 to 8, in some embodiments, from 0 to 2, and
in one embodiment, 0; and
n is from 2 to 5,000, in some embodiments from 4 to 2,000, and in
some embodiments, from 5 to 1,000. Example of substituents for the
radicals "D" or "R.sub.7" include, for instance, alkyl, cycloalkyl,
aryl, aralkyl, alkoxy, halogen, ether, thioether, disulphide,
sulfoxide, sulfone, sulfonate, amino, aldehyde, keto, carboxylic
acid ester, carboxylic acid, carbonate, carboxylate, cyano,
alkylsilane and alkoxysilane groups, carboxylamide groups, and so
forth.
Particularly suitable thiophene polymers are those in which "D" is
an optionally substituted C.sub.2 to C.sub.3 alkylene radical. For
instance, the polymer may be optionally substituted
poly(3,4-ethylenedioxythiophene), which has the following general
structure:
##STR00002##
Methods for forming conductive polymers, such as described above,
are well known in the art. For instance, U.S. Pat. No. 6,987,663 to
Merker, et al., which is incorporated herein in its entirety by
reference thereto for all purposes, describes various techniques
for forming substituted polythiophenes from a monomeric precursor.
The monomeric precursor may, for instance, have the following
structure:
##STR00003## wherein,
T, D, R.sub.7, and q are defined above. Particularly suitable
thiophene monomers are those in which "D" is an optionally
substituted C.sub.2 to C.sub.3 alkylene radical. For instance,
optionally substituted 3,4-alkylenedioxythiophenes may be employed
that have the general structure:
##STR00004##
wherein, R.sub.7 and q are as defined above. In one particular
embodiment, "q" is 0. One commercially suitable example of
3,4-ethylenedioxthiophene is available from Heraeus Clevios under
the designation Clevios.TM. M. Other suitable monomers are also
described in U.S. Pat. Nos. 5,111,327 to Blohm, et al. and
6,635,729 to Groenendaal, et al., which are incorporated herein in
their entirety by reference thereto for all purposes. Derivatives
of these monomers may also be employed that are, for example,
dimers or trimers of the above monomers. Higher molecular
derivatives, i.e., tetramers, pentamers, etc. of the monomers are
suitable for use in the present invention. The derivatives may be
made up of identical or different monomer units and used in pure
form and in a mixture with one another and/or with the monomers.
Oxidized or reduced forms of these precursors may also be
employed.
The thiophene monomers are chemically polymerized in the presence
of an oxidative catalyst. The oxidative catalyst typically includes
a transition metal cation, such as iron(III), copper(II),
chromium(VI), cerium(IV), manganese(IV), manganese(VII),
ruthenium(III) cations, etc. A dopant may also be employed to
provide excess charge to the conductive polymer and stabilize the
conductivity of the polymer. The dopant typically includes an
inorganic or organic anion, such as an ion of a sulfonic acid. In
certain embodiments, the oxidative catalyst employed in the
precursor solution has both a catalytic and doping functionality in
that it includes a cation (e.g., transition metal) and anion (e.g.,
sulfonic acid). For example, the oxidative catalyst may be a
transition metal salt that includes iron(III) cations, such as
iron(III) halides (e.g., FeCl.sub.3) or iron(III) salts of other
inorganic acids, such as Fe(ClO.sub.4).sub.3 or
Fe.sub.2(SO.sub.4).sub.3 and the iron(III) salts of organic acids
and inorganic acids comprising organic radicals. Examples of iron
(III) salts of inorganic acids with organic radicals include, for
instance, iron(III) salts of sulfuric acid monoesters of C.sub.1 to
C.sub.20 alkanols (e.g., iron(III) salt of lauryl sulfate).
Likewise, examples of iron(III) salts of organic acids include, for
instance, iron(III) salts of C.sub.1 to C.sub.20 alkane sulfonic
acids (e.g., methane, ethane, propane, butane, or dodecane sulfonic
acid); iron (III) salts of aliphatic perfluorosulfonic acids (e.g.,
trifluoromethane sulfonic acid, perfluorobutane sulfonic acid, or
perfluorooctane sulfonic acid); iron (III) salts of aliphatic
C.sub.1 to C.sub.20 carboxylic acids (e.g., 2-ethylhexylcarboxylic
acid); iron (III) salts of aliphatic perfluorocarboxylic acids
(e.g., trifluoroacetic acid or perfluorooctane acid); iron (III)
salts of aromatic sulfonic acids optionally substituted by C.sub.1
to C.sub.20 alkyl groups (e.g., benzene sulfonic acid, o-toluene
sulfonic acid, p-toluene sulfonic acid, or dodecylbenzene sulfonic
acid); iron (III) salts of cycloalkane sulfonic acids (e.g.,
camphor sulfonic acid); and so forth. Mixtures of these
above-mentioned iron(III) salts may also be used.
Iron(III)-p-toluene sulfonate, iron(III)-o-toluene sulfonate, and
mixtures thereof, are particularly suitable. One commercially
suitable example of iron(III)-p-toluene sulfonate is available from
Heraeus Clevios under the designation Clevios.TM. C.
Various methods may be utilized to form a conductive polymer layer.
In one embodiment, the oxidative catalyst and monomer are applied,
either sequentially or together, such that the polymerization
reaction occurs in situ on the part. Suitable application
techniques may include screen-printing, dipping, electrophoretic
coating, and spraying, may be used to form a conductive polymer
coating. As an example, the monomer may initially be mixed with the
oxidative catalyst to form a precursor solution. Once the mixture
is formed, it may be applied to the part and then allowed to
polymerize so that the conductive coating is formed on the surface.
Alternatively, the oxidative catalyst and monomer may be applied
sequentially. In one embodiment, for example, the oxidative
catalyst is dissolved in an organic solvent (e.g., butanol) and
then applied as a dipping solution. The part may then be dried to
remove the solvent therefrom. Thereafter, the part may be dipped
into a solution containing the monomer.
Polymerization is typically performed at temperatures of from about
-10.degree. C. to about 250.degree. C., and in some embodiments,
from about 0.degree. C. to about 200.degree. C., depending on the
oxidizing agent used and desired reaction time. Suitable
polymerization techniques, such as described above, may be
described in more detail in U.S. Pat. No. 7,515,396 to Biler. Still
other methods for applying such conductive coating(s) may be
described in U.S. Pat. Nos. 5,457,862 to Sakata, et al., 5,473,503
to Sakata, et al., 5,729,428 to Sakata, et al., and 5,812,367 to
Kudoh, et al., which are incorporated herein in their entirety by
reference thereto for all purposes.
In addition to in situ application, a conductive polymer layer may
also be applied in the form of a dispersion of conductive polymer
particles. Although their size may vary, it is typically desired
that the particles possess a small diameter to increase the surface
area available for adhering to the anode part. For example, the
particles may have an average diameter of from about 1 to about 500
nanometers, in some embodiments from about 5 to about 400
nanometers, and in some embodiments, from about 10 to about 300
nanometers. The D.sub.90 value of the particles (particles having a
diameter of less than or equal to the D.sub.90 value constitute 90%
of the total volume of all of the solid particles) may be about 15
micrometers or less, in some embodiments about 10 micrometers or
less, and in some embodiments, from about 1 nanometer to about 8
micrometers. The diameter of the particles may be determined using
known techniques, such as by ultracentrifuge, laser diffraction,
etc.
The formation of the conductive polymers into a particulate form
may be enhanced by using a separate counterion to counteract the
positive charge carried by the substituted polythiophene. In some
cases, the polymer may possess positive and negative charges in the
structural unit, with the positive charge being located on the main
chain and the negative charge optionally on the substituents of the
radical "R", such as sulfonate or carboxylate groups. The positive
charges of the main chain may be partially or wholly saturated with
the optionally present anionic groups on the radicals "R." Viewed
overall, the polythiophenes may, in these cases, be cationic,
neutral or even anionic. Nevertheless, they are all regarded as
cationic polythiophenes as the polythiophene main chain has a
positive charge.
The counterion may be a monomeric or polymeric anion. Polymeric
anions can, for example, be anions of polymeric carboxylic acids
(e.g., polyacrylic acids, polymethacrylic acid, polymaleic acids,
etc.); polymeric sulfonic acids (e.g., polystyrene sulfonic acids
("PSS"), polyvinyl sulfonic acids, etc.); and so forth. The acids
may also be copolymers, such as copolymers of vinyl carboxylic and
vinyl sulfonic acids with other polymerizable monomers, such as
acrylic acid esters and styrene. Likewise, suitable monomeric
anions include, for example, anions of C.sub.1 to C.sub.20 alkane
sulfonic acids (e.g., dodecane sulfonic acid); aliphatic
perfluorosulfonic acids (e.g., trifluoromethane sulfonic acid,
perfluorobutane sulfonic acid or perfluorooctane sulfonic acid);
aliphatic C.sub.1 to C.sub.20 carboxylic acids (e.g.,
2-ethyl-hexylcarboxylic add); aliphatic perfluorocarboxylic acids
(e.g., trifluoroacetic acid or perfluorooctanoic acid); aromatic
sulfonic acids optionally substituted by C.sub.1 to C.sub.20 alkyl
groups (e.g., benzene sulfonic acid, o-toluene sulfonic acid,
p-toluene sulfonic acid or dodecylbenzene sulfonic acid);
cycloalkane sulfonic acids (e.g., camphor sulfonic acid or
tetrafluoroborates, hexafluorophosphates, perchiorates,
hexafluoroantimonates, hexafluoroarsenates or
hexachloroantimonates); and so forth. Particularly suitable
counteranions are polymeric anions, such as a polymeric carboxylic
or sulfonic acid (e.g., polystyrene sulfonic acid ("PSS")). The
molecular weight of such polymeric anions typically ranges from
about 1,000 to about 2,000,000, and in some embodiments, from about
2,000 to about 500,000.
When employed, the weight ratio of such counterions to substituted
polythiophenes in a given layer is typically from about 0.5:1 to
about 50:1, in some embodiments from about 1:1 to about 30:1, and
in some embodiments, from about 2:1 to about 20:1. The weight of
the substituted polythiophene referred to in the above-referenced
weight ratios refers to the weighed-in portion of the monomers
used, assuming that a complete conversion occurs during
polymerization.
The dispersion may also contain one or more binders to further
enhance the adhesive nature of the polymeric layer and also
increase the stability of the particles within the dispersion. The
binders may be organic in nature, such as polyvinyl alcohols,
polyvinyl pyrrolidones, polyvinyl chlorides, polyvinyl acetates,
polyvinyl butyrates, polyacrylic acid esters, polyacrylic acid
amides, polymethacrylic acid esters, polymethacrylic acid amides,
polyacrylonitriles, styrene/acrylic acid ester, vinyl
acetate/acrylic acid ester and ethylene/vinyl acetate copolymers,
polybutadienes, polyisoprenes, polystyrenes, polyethers,
polyesters, polycarbonates, polyurethanes, polyamides, polyimides,
polysulfones, melamine formaldehyde resins, epoxide resins,
silicone resins or celluloses. Crosslinking agents may also be
employed to enhance the adhesion capacity of the binders. Such
crosslinking agents may include, for instance, melamine compounds,
masked isocyanates or functional silanes, such as
3-glycidoxypropyltrialkoxysilane, tetraethoxysilane and
tetraethoxysilane hydrolysate or crosslinkable polymers, such as
polyurethanes, polyacrylates or polyolefins, and subsequent
crosslinking. Other components may also be included within the
dispersion as is known in the art, such as dispersion agents (e.g.,
water), surface-active substances, etc.
If desired, one or more of the above-described application steps
may be repeated until the desired thickness of the coating is
achieved. In some embodiments, only a relatively thin layer of the
coating is formed at a time. The total target thickness of the
coating may generally vary depending on the desired properties of
the capacitor. Typically, the resulting conductive polymer coating
has a thickness of from about 0.2 micrometers (".mu.m") to about 50
.mu.m, in some embodiments from about 0.5 .mu.m to about 20 .mu.m,
and in some embodiments, from about 1 .mu.m to about 5 .mu.m. It
should be understood that the thickness of the coating is not
necessarily the same at all locations on the part. Nevertheless,
the average thickness of the coating on the substrate generally
falls within the ranges noted above.
The conductive polymer layer may optionally be healed. Healing may
occur after each application of a conductive polymer layer or may
occur after the application of the entire coating. In some
embodiments, the conductive polymer can be healed by dipping the
part into an electrolyte solution, and thereafter applying a
constant voltage to the solution until the current is reduced to a
preselected level. If desired, such healing can be accomplished in
multiple steps. For example, an electrolyte solution can be a
dilute solution of the monomer, the catalyst, and dopant in an
alcohol solvent (e.g., ethanol). The coating may also be washed if
desired to remove various byproducts, excess reagents, and so
forth.
If desired, the capacitor may also contain other layers as is known
in the art. For example, a protective coating may optionally be
formed between the dielectric and solid electrolyte, such as one
made of a relatively insulative resinous material (natural or
synthetic). Such materials may have a specific resistivity of
greater than about 10 .OMEGA./cm, in some embodiments greater than
about 100, in some embodiments greater than about 1,000 .OMEGA./cm,
in some embodiments greater than about 1.times.10.sup.5 .OMEGA./cm,
and in some embodiments, greater than about 1.times.10.sup.10
.OMEGA./cm. Some resinous materials that may be utilized in the
present invention include, but are not limited to, polyurethane,
polystyrene, esters of unsaturated or saturated fatty acids (e.g.,
glycerides), and so forth. For instance, suitable esters of fatty
acids include, but are not limited to, esters of lauric acid,
myristic acid, palmitic acid, stearic acid, eleostearic acid, oleic
acid, linoleic acid, linolenic acid, aleuritic acid, shellolic
acid, and so forth. These esters of fatty acids have been found
particularly useful when used in relatively complex combinations to
form a "drying oil", which allows the resulting film to rapidly
polymerize into a stable layer. Such drying oils may include mono-,
di-, and/or tri-glycerides, which have a glycerol backbone with
one, two, and three, respectively, fatty acyl residues that are
esterified. For instance, some suitable drying oils that may be
used include, but are not limited to, olive oil, linseed oil,
castor oil, tung oil, soybean oil, and shellac. These and other
protective coating materials are described in more detail U.S. Pat.
No. 6,674,635 to Fife, et al., which is incorporated herein in its
entirety by reference thereto for all purposes.
The part may also be applied with a carbon layer (e.g., graphite)
and silver layer, respectively. The silver coating may, for
instance, act as a solderable conductor, contact layer, and/or
charge collector for the capacitor and the carbon coating may limit
contact of the silver coating with the solid electrolyte. Such
coatings may cover some or all of the solid electrolyte.
Generally speaking, the capacitor element is substantially free of
resins that encapsulate the capacitor element as are often employed
in conventional solid electrolytic capacitors. Among other things,
the encapsulation of the capacitor element can lead to instability
in extreme environments, i.e., high temperature (e.g., above about
175.degree. C.) and/or high voltage (e.g., above about 35
volts).
II. Housing
As indicated above, the capacitor element is hermetically sealed
within a housing. Any of a variety of different materials may be
used to form the housing, such as metals, plastics, ceramics, and
so forth. In one embodiment, for example, the housing includes one
or more layers of a metal, such as tantalum, niobium, aluminum,
nickel, hafnium, titanium, copper, silver, steel (e.g., stainless),
alloys thereof (e.g., electrically conductive oxides), composites
thereof (e.g., metal coated with electrically conductive oxide),
and so forth. In another embodiment, the housing may include one or
more layers of a ceramic material, such as aluminum nitride,
aluminum oxide, silicon oxide, magnesium oxide, calcium oxide,
glass, etc., as well as combinations thereof.
The housing may have any desired shape, such as cylindrical,
D-shaped, rectangular, triangular, prismatic, etc. Referring to
FIG. 1, for example, one embodiment of a capacitor assembly 200 is
shown that contains a housing 222 and a capacitor element 120. In
this particular embodiment, the housing 222 is generally
rectangular. Typically, the housing and the capacitor element have
the same or similar shape so that the capacitor element can be
readily accommodated within the interior cavity. In the illustrated
embodiment, for example, both the capacitor element 120 and the
housing 222 have a generally rectangular shape.
If desired, the capacitor assembly of the present invention may
exhibit a relatively high volumetric efficiency. To facilitate such
high efficiency, the capacitor element typically occupies a
substantial portion of the volume of an interior cavity of the
housing. For example, the capacitor element may occupy about 30
vol. % or more, in some embodiments about 50 vol. % or more, in
some embodiments about 60 vol. % or more, in some embodiments about
70 vol. % or more, in some embodiments from about 80 vol. % to
about 98 vol. %, and in some embodiments, from about 85 vol. % to
97 vol. % of the interior cavity of the housing. To this end, the
difference between the dimensions of the capacitor element and
those of the interior cavity defined by the housing are typically
relatively small.
Referring to FIG. 1, for example, the capacitor element 120 may
have a length (excluding the length of the anode lead 6) that is
relatively similar to the length of an interior cavity 126 defined
by the housing 222. For example, the ratio of the length of the
anode to the length of the interior cavity ranges from about 0.40
to 1.00, in some embodiments from about 0.50 to about 0.99, in some
embodiments from about 0.60 to about 0.99, and in some embodiments,
from about 0.70 to about 0.98. The capacitor element 120 may have a
length of from about 5 to about 10 millimeters, and the interior
cavity 126 may have a length of from about 6 to about 15
millimeters. Similarly, the ratio of the height of the capacitor
element 120 (in the -z direction) to the height of the interior
cavity 126 may range from about 0.40 to 1.00, in some embodiments
from about 0.50 to about 0.99, in some embodiments from about 0.60
to about 0.99, and in some embodiments, from about 0.70 to about
0.98. The ratio of the width of the capacitor element 120 (in the
-x direction) to the width of the interior cavity 126 may also
range from about 0.50 to 1.00, in some embodiments from about 0.60
to about 0.99, in some embodiments from about 0.70 to about 0.99,
in some embodiments from about 0.80 to about 0.98, and in some
embodiments, from about 0.85 to about 0.95. For example, the width
of the capacitor element 120 may be from about 2 to about 7
millimeters and the width of the interior cavity 126 may be from
about 3 to about 10 millimeters, and the height of the capacitor
element 120 may be from about 0.5 to about 2 millimeters and the
width of the interior cavity 126 may be from about 0.7 to about 6
millimeters.
Although by no means required, the capacitor element may be
attached to the housing in such a manner that an anode termination
and cathode termination are formed external to the housing for
subsequent integration into a circuit. The particular configuration
of the terminations may depend on the intended application. In one
embodiment, for example, the capacitor assembly may be formed so
that it is surface mountable, and yet still mechanically robust.
For example, the anode lead may be electrically connected to
external, surface mountable anode and cathode terminations (e.g.,
pads, sheets, plates, frames, etc.). Such terminations may extend
through the housing to connect with the capacitor. The thickness or
height of the terminations is generally selected to minimize the
thickness of the capacitor assembly. For instance, the thickness of
the terminations may range from about 0.05 to about 1 millimeter,
in some embodiments from about 0.05 to about 0.5 millimeters, and
from about 0.1 to about 0.2 millimeters. If desired, the surface of
the terminations may be electroplated with nickel, silver, gold,
tin, etc. as is known in the art to ensure that the final part is
mountable to the circuit board. In one particular embodiment, the
termination(s) are deposited with nickel and silver flashes,
respectively, and the mounting surface is also plated with a tin
solder layer. In another embodiment, the termination(s) are
deposited with thin outer metal layers (e.g., gold) onto a base
metal layer (e.g., copper alloy) to further increase
conductivity.
In certain embodiments, connective members may be employed within
the interior cavity of the housing to facilitate connection to the
terminations in a mechanically stable manner. For example,
referring again to FIG. 1, the capacitor assembly 200 may include a
connection member 162 that is formed from a first portion 167 and a
second portion 165. The connection member 162 may be formed from
conductive materials similar to the external terminations. The
first portion 167 and second portion 165 may be integral or
separate pieces that are connected together, either directly or via
an additional conductive element (e.g., metal). In the illustrated
embodiment, the second portion 165 is provided in a plane that is
generally parallel to a lateral direction in which the lead 6
extends (e.g., -y direction). The first portion 167 is "upstanding"
in the sense that it is provided in a plane that is generally
perpendicular the lateral direction in which the lead 6 extends. In
this manner, the first portion 167 can limit movement of the lead 6
in the horizontal direction to enhance surface contact and
mechanical stability during use. If desired, an insulative material
7 (e.g. Teflon.TM. washer) may be employed around the lead 6.
The first portion 167 may possess a mounting region (not shown)
that is connected to the anode lead 6. The region may have a
"U-shape" for further enhancing surface contact and mechanical
stability of the lead 6. Connection of the region to the lead 6 may
be accomplished using any of a variety of known techniques, such as
welding, laser welding, conductive adhesives, etc. In one
particular embodiment, for example, the region is laser welded to
the anode lead 6. Regardless of the technique chosen, however, the
first portion 167 can hold the anode lead 6 in substantial
horizontal alignment to further enhance the dimensional stability
of the capacitor assembly 200.
Referring again to FIG. 1, one embodiment of the present invention
is shown in which the connective member 162 and capacitor element
120 are connected to the housing 222 through anode and cathode
terminations 127 and 129, respectively. The anode termination 127
contains a first region 127a that is positioned within the housing
222 and electrically connected to the connection member 162 and a
second region 127b that is positioned external to the housing 222
and provides a mounting surface 201. Likewise, the cathode
termination 129 contains a first region 129a that is positioned
within the housing 222 and electrically connected to the solid
electrolyte of the capacitor element 120 and a second region 129b
that is positioned external to the housing 222 and provides a
mounting surface 203. It should be understood that the entire
portion of such regions need not be positioned within or external
to the housing.
In the illustrated embodiment, a conductive trace 127c extends in a
base 123 of the housing to connect the first region 127a and second
region 127b. Similarly, a conductive trace 129c extends in the base
123 of the housing to connect the first region 127a and second
region 127b. The conductive traces and/or regions of the
terminations may be separate or integral. In addition to extending
through the outer wall of the housing, the traces may also be
positioned at other locations, such as external to the outer wall.
Of course, the present invention is by no means limited to the use
of conductive traces for forming the desired terminations.
Regardless of the particular configuration employed, connection of
the terminations 127 and 129 to the capacitor element 120 may be
made using any known technique, such as welding, laser welding,
conductive adhesives, etc. In one particular embodiment, for
example, a conductive adhesive 131 is used to connect the second
portion 165 of the connection member 162 to the anode termination
127. Likewise, a conductive adhesive 133 is used to connect the
cathode of the capacitor element 120 to the cathode termination
129. The conductive adhesives may be formed from conductive metal
particles contained with a resin composition. The metal particles
may be silver, copper, gold, platinum, nickel, zinc, bismuth, etc.
The resin composition may include a thermoset resin (e.g., epoxy
resin), curing agent (e.g., acid anhydride), and coupling agent
(e.g., silane coupling agents). Suitable conductive adhesives are
described in U.S. Patent Application Publication No. 2006/0038304
to Osaka, et al., which is incorporated herein in its entirety by
reference thereto for all purposes.
Optionally, a polymeric restraint may also be disposed in contact
with one or more surfaces of the capacitor element, such as the
rear surface, front surface, upper surface, lower surface, side
surface(s), or any combination thereof. The polymeric restraint can
reduce the likelihood of delamination by the capacitor element from
the housing. In this regard, the polymeric restraint may possesses
a certain degree of strength that allows it to retain the capacitor
element in a relatively fixed positioned even when it is subjected
to vibrational forces, yet is not so strong that it cracks. For
example, the restraint may possess a tensile strength of from about
1 to about 150 Megapascals ("MPa"), in some embodiments from about
2 to about 100 MPa, in some embodiments from about 10 to about 80
MPa, and in some embodiments, from about 20 to about 70 MPa,
measured at a temperature of about 25.degree. C. It is normally
desired that the restraint is not electrically conductive.
Although any of a variety of materials may be employed that have
the desired strength properties noted above, curable thermosetting
resins have been found to be particularly suitable for use in the
present invention. Examples of such resins include, for instance,
epoxy resins, polyimides, melamine resins, urea-formaldehyde
resins, polyurethanes, silicone polymers, phenolic resins, etc. In
certain embodiments, for example, the restraint may employ one or
more polyorganosiloxanes. Silicon-bonded organic groups used in
these polymers may contain monovalent hydrocarbon and/or monovalent
halogenated hydrocarbon groups. Such monovalent groups typically
have from 1 to about 20 carbon atoms, preferably from 1 to 10
carbon atoms, and are exemplified by, but not limited to, alkyl
(e.g., methyl, ethyl, propyl, pentyl, octyl, undecyl, and
octadecyl); cycloalkyl (e.g., cyclohexyl); alkenyl (e.g., vinyl,
allyl, butenyl, and hexenyl); aryl (e.g., phenyl, tolyl, xylyl,
benzyl, and 2-phenylethyl); and halogenated hydrocarbon groups
(e.g., 3,3,3-trifluoropropyl, 3-chloropropyl, and dichlorophenyl).
Typically, at least 50%, and more preferably at least 80%, of the
organic groups are methyl. Examples of such methylpolysiloxanes may
include, for instance, polydimethylsiloxane ("PDMS"),
polymethylhydrogensiloxane, etc. Still other suitable methyl
polysiloxanes may include dimethyldiphenylpolysiloxane,
dimethyl/methylphenylpolysiloxane, polymethylphenylsiloxane,
methylphenyl/dimethylsiloxane, vinyldimethyl terminated
polydimethylsiloxane, vinylmethyl/dimethylpolysiloxane,
vinyldimethyl terminated vinylmethyl/dimethylpolysiloxane,
divinylmethyl terminated polydimethylsiloxane, vinylphenylmethyl
terminated polydimethylsiloxane, dimethylhydro terminated
polydimethylsiloxane, methylhydro/dimethylpolysiloxane, methylhydro
terminated methyloctylpolysiloxane, methylhydro/phenylmethyl
polysiloxane, etc.
The organopolysiloxane may also contain one more pendant and/or
terminal polar functional groups, such as hydroxyl, epoxy,
carboxyl, amino, alkoxy, methacrylic, or mercapto groups, which
impart some degree of hydrophilicity to the polymer. For example,
the organopolysiloxane may contain at least one hydroxy group, and
optionally an average of at least two silicon-bonded hydroxy groups
(silanol groups) per molecule. Examples of such organopolysiloxanes
include, for instance, dihydroxypolydimethylsiloxane,
hydroxy-trimethylsiloxypolydimethylsiloxane, etc. Other examples of
hydroxyl-modified organopolysiloxanes are described in U.S. Patent
Application Publication No. 2003/0105207 to Kleyer, et al., which
is incorporated herein in its entirety by reference thereto for all
purposes. Alkoxy-modified organopolysiloxanes may also be employed,
such as dimethoxypolydimethylsiloxane,
methoxy-trimethylsiloxypolydimethylsiloxane,
diethoxypolydimethylsiloxane,
ethoxy-trimethylsiloxy-polydimethylsiloxane, etc. Still other
suitable organopolysiloxanes are those modified with at least one
amino functional group. Examples of such amino-functional
polysiloxanes include, for instance, diamino-functional
polydimethylsiloxanes. Various other suitable polar functional
groups for organopolysiloxanes are also described in U.S. Patent
Application Publication No. 2010/00234517 to Plantenberg, et al.,
which is incorporated herein in its entirety by reference thereto
for all purposes.
Epoxy resins are also particularly suitable for use as the
polymeric restraint. Examples of suitable epoxy resins include, for
instance, glycidyl ether type epoxy resins, such as bisphenol A
type epoxy resins, bisphenol F type epoxy resins, phenol novolac
type epoxy resins, orthocresol novolac type epoxy resins,
brominated epoxy resins and biphenyl type epoxy resins, cyclic
aliphatic epoxy resins, glycidyl ester type epoxy resins,
glycidylamine type epoxy resins, cresol novolac type epoxy resins,
naphthalene type epoxy resins, phenol aralkyl type epoxy resins,
cyclopentadiene type epoxy resins, heterocyclic epoxy resins, etc.
Still other suitable conductive adhesive resins may also be
described in U.S. Patent Application Publication No. 2006/0038304
to Osako, et al. and U.S. Pat. No. 7,554,793 to Chacko, which are
incorporated herein in their entirety by reference thereto for all
purposes.
If desired, curing agents may also be employed in the polymeric
restraint to help promote curing. The curing agents typically
constitute from about 0.1 to about 20 wt. % of the restraint.
Exemplary curing agents include, for instance, amines, peroxides,
anhydrides, phenol compounds, silanes, acid anhydride compounds and
combinations thereof. Specific examples of suitable curing agents
are dicyandiamide, 1-(2 cyanoethyl) 2-ethyl-4-methylimidazole,
1-benzyl 2-methylimidazole, ethyl cyano propyl imidazole,
2-methylimidazole, 2-phenylimidazole, 2-ethyl-4-methylimidazole,
2-undecylimidazole, 1-cyanoethyl-2-methylimidazole,
2,4-dicyano-6,2-methylimidazolyl-(1)-ethyl-s-triazine, and
2,4-dicyano-6,2-undecylimidazolyl-(1)-ethyl-s-triazine, imidazolium
salts (such as 1-cyanoethyl-2-undecylimidazolium trimellitate,
2-methylimidazolium isocyanurate, 2-ethyl-4-methylimidazolium
tetraphenylborate, and 2-ethyl-1,4-dimethylimidazolium
tetraphenylborate, etc. Still other useful curing agents include
phosphine compounds, such as tributylphosphine, triphenylphosphine,
tris(dimethoxyphenyl)phosphine, tris(hydroxypropyl)phosphine, and
tris(cyanoethyl)phsphine; phosphonium salts, such as
tetraphenylphosphonium-tetraphenylborate,
methyltributylphosphonium-tetraphenylborate, and
methyltricyanoethylphosphonium tetraphenylborate); amines, such as
2,4,6-tris(dimethylaminomethyl)phenol, benzylmethylamine,
tetramethylbutylguanidine, N-methylpiperazine, and
2-dimethylamino-1-pyrroline, ammonium salts, such as
triethylammonium tetraphenylborate; diazabicyclo compounds, such as
1,5-diazabicyclo[5,4,0]-7-undecene,
1,5-diazabicyclo[4,3,0]-5-nonene, and
1,4-diazabicyclo[2,2,2]-octane; salts of diazabicyclo compounds
such as tetraphenylborate, phenol salt, phenolnovolac salt, and
2-ethylhexanoic acid salt; and so forth.
Still other additives may also be employed, such as
photoinitiators, viscosity modifiers, suspension aiding agents,
pigments, stress reducing agents, coupling agents (e.g., silane
coupling agents), nonconductive fillers (e.g., clay, silica,
alumina, etc.), stabilizers, etc. Suitable photoinitiators may
include, for instance, benzoin, benzoin methyl ether, benzoin ethyl
ether, benzoin n-propyl ether, benzoin isobutyl ether, 2,2
dihydroxy-2-phenylacetophenone, 2,2-dimethoxy-2-phenylacetophenone
2,2-diethoxy-2-phenylacetophenone, 2,2-diethoxyacetophenone,
benzophenone, 4,4-bisdialylaminobenzophenone,
4-dimethylaminobenzoic acid, alkyl 4-dimethylaminobenzoate,
2-ethylanthraquinone, xanthone, thioxanthone,
2-cholorothioxanthone, etc. When employed, such additives typically
constitute from about 0.1 to about 20 wt. % of the total
composition.
Referring again to FIG. 1, for instance, one embodiment is shown in
which a single polymeric restraint 197 is disposed in contact with
an upper surface 181 and rear surface 177 of the capacitor element
120. While a single restraint is shown in FIG. 1, it should be
understood that separate restraints may be employed to accomplish
the same function. In fact, more generally, any number of polymeric
restraints may be employed to contact any desired surface of the
capacitor element. When multiple restraints are employed, they may
be in contact with each other or remain physically separated. For
example, in one embodiment, a second polymeric restraint (not
shown) may be employed that contacts the upper surface 181 and
front surface 179 of the capacitor element 120. The first polymeric
restraint 197 and the second polymeric restraint (not shown) may or
may not be in contact with each other. In yet another embodiment, a
polymeric restraint may also contact a lower surface 183 and/or
side surface(s) of the capacitor element 120, either in conjunction
with or in lieu of other surfaces.
Regardless of how it is applied, it is typically desired that the
polymeric restraint is also in contact with at least one surface of
the housing to help further mechanically stabilize the capacitor
element against possible delamination. For example, the restraint
may be in contact with an interior surface of one or more
sidewall(s), outer wall, lid, etc. In FIG. 1, for example, the
polymeric restraint 197 is in contact with interior surfaces 107
and 109 of the housing 222. While in contact with the housing, it
is nevertheless desired that at least a portion of the cavity
defined by the housing remains unoccupied to allow for the inert
gas to flow through the cavity and limit contact of the solid
electrolyte with oxygen. For example, at least about 5% of the
cavity volume typically remains unoccupied by the capacitor element
and polymer restraint, and in some embodiments, from about 10% to
about 50% of the cavity volume.
Once connected in the desired manner, the resulting package is
hermetically sealed. Referring again to FIG. 1, for instance, the
housing 222 includes a base 123 and a lid 225 between which the
cavity 126 is formed. The lid 225 and base 123 may be formed from a
ceramic, metal (e.g., iron, copper, nickel, cobalt, etc., as well
as alloys thereof), plastic, and so forth. In one embodiment, for
example, the base 123 is formed from a ceramic material and the lid
225 is formed from a metal material. The lid 225 includes an outer
wall 223 that is integral with at least one sidewall 224. In the
illustrated embodiment, for example, two opposing sidewalls 224 are
shown in cross-section. The height of the sidewall(s) 224 is
generally such that the lid 225 does not contact any surface of the
capacitor element 120 so that it is not contaminated. The outer
wall 223 and base 123 both extend in a lateral direction (-y
direction) and are generally parallel with each other and to the
lateral direction of the anode lead 6. The sidewall 224 extends
from the outer wall 223 in a longitudinal direction that is
generally perpendicular to the base 123. A distal end 500 of the
lid 225 is defined by the outer wall 223 and a proximal end 501 is
defined by a lip 253 of the sidewall 224.
FIG. 2 shows the lip 253 in more detail. More particularly, the
sidewall 224 has a thickness in a lateral direction defined between
surfaces 403 and 405. The lip 253 extends from the sidewall 224 in
the lateral direction, which may be generally parallel to the
lateral direction of the base 123. The angle .alpha. between the
sidewall 224 and the lip 253 may vary, but is typically from about
60.degree. to about 120.degree., in some embodiments from about
70.degree. to about 110.degree., and in some embodiments, from
about 80.degree. to about 100.degree. (e.g., about 90.degree.). The
lip 253 also defines a peripheral edge 251, which may be generally
perpendicular to the lateral direction in which the lip 253 and
base 123 extend. The peripheral edge 251 is located beyond the
outer periphery of the sidewall 224 and may be generally coplanar
with an edge 151 of the base 123. The lip 253 may be sealed to the
base 123 using any known technique, such as welding (e.g.,
resistance or laser), soldering, glue, etc. For example, in the
illustrated embodiment, a sealing member 287 is employed (e.g.,
glass-to-metal seal, Kovar.RTM. ring, etc.) between the components
to facilitate their attachment. Regardless, the use of a lip
described above can enable a more stable connection between the
components and improve the seal and mechanical stability of the
capacitor assembly.
Hermetic sealing typically occurs in the presence of a gaseous
atmosphere that contains at least one inert gas so as to inhibit
oxidation of the solid electrolyte during use. The inert gas may
include, for instance, nitrogen, helium, argon, xenon, neon,
krypton, radon, and so forth, as well as mixtures thereof.
Typically, inert gases constitute the majority of the atmosphere
within the housing, such as from about 50 wt. % to 100 wt. %, in
some embodiments from about 75 wt. % to 100 wt. %, and in some
embodiments, from about 90 wt. % to about 99 wt. % of the
atmosphere. If desired, a relatively small amount of non-inert
gases may also be employed, such as carbon dioxide, oxygen, water
vapor, etc. In such cases, however, the non-inert gases typically
constitute 15 wt. % or less, in some embodiments 10 wt. % or less,
in some embodiments about 5 wt. % or less, in some embodiments
about 1 wt. % or less, and in some embodiments, from about 0.01 wt.
% to about 1 wt. % of the atmosphere within the housing. For
example, the moisture content (expressed in terms of relatively
humidity) may be about 10% or less, in some embodiments about 5% or
less, in some embodiments about 1% or less, and in some
embodiments, from about 0.01 to about 5%.
It should be understood that the embodiments described are only
exemplary, and that various other configurations may be employed in
the present invention. For example, FIG. 3 shows a capacitor
assembly 300 having a housing configuration similar to that of
FIGS. 1-2, except that terminal pins 327b and 329b are employed as
the external terminations for the anode and cathode, respectively.
More particularly, the terminal pin 327a extends through a trace
327c formed in the outer wall 323 and is connected to the anode
lead 6 using known techniques (e.g., welding). An additional
section 327a may be employed to secure the pin 327b. Likewise, the
terminal pin 329b extends through a trace 329c formed in the outer
wall 323 and is connected to the cathode via a conductive adhesive
133 as described above.
The embodiments shown in FIGS. 1-3 are discussed herein in terms of
only a single capacitor element. It should also be understood,
however, that multiple capacitor elements may also be hermetically
sealed within a housing. The multiple capacitor elements may be
attached to the housing any of a variety of different
techniques.
As a result of the present invention, the capacitor assembly may
exhibit excellent electrical properties even when exposed to high
temperature and high voltage environments. For example, the
capacitor assembly may exhibit a relatively high "breakdown
voltage" (voltage at which the capacitor fails), such as about 35
volts or more, in some embodiments about 50 volts or more, in some
embodiments about 60 volts or more, and in some embodiments, from
about 60 volts to about 100 volts, such as determined by increasing
the applied voltage in increments of 3 volts until the leakage
current reaches 1 mA. Likewise, the capacitor may also be able to
withstand relatively high surge currents, which is also common in
high voltage applications. The peak surge current may, for example,
about 2 times the rated voltage or more, such as range from about
40 Amps or more, in some embodiments about 60 Amps or more, and in
some embodiments, and in some embodiments, from about 120 Amps to
about 250 Amps.
The capacitance may likewise be about 1 milliFarad per square
centimeter ("mF/cm.sup.2") or more, in some embodiments about 2
mF/cm.sup.2 or more, in some embodiments from about 5 to about 50
mF/cm.sup.2, and in some embodiments, from about 8 to about 20
mF/cm.sup.2. The capacitance may be determined at an operating
frequency of 120 Hz and a temperature of 25.degree. C. In addition,
the capacitor assembly can also exhibit a relatively high
percentage of its wet capacitance, which enables it to have only a
small capacitance loss and/or fluctuation in the presence of
atmosphere humidity. This performance characteristic is quantified
by the "dry to wet capacitance percentage", which is determined by
the equation: Dry to Wet
Capacitance=(1-([Wet-Dry]/Wet)).times.100
The capacitor assembly of the present invention, for instance, may
exhibit a dry to wet capacitance percentage of about 80% or more,
in some embodiments about 85% or more, in some embodiments about
90% or more, and in some embodiments, from about 92% to 100%.
The capacitor assembly may also have an equivalence series
resistance ("ESR") of less than about 50 ohms, in some embodiments
less than about 25 ohms, in some embodiments from about 0.01 to
about 10 ohms, and in some embodiments, from about 0.05 to about 5
ohms, measured at an operating frequency of 100 kHz. In addition,
the leakage current, which generally refers to the current flowing
from one conductor to an adjacent conductor through an insulator,
can be maintained at relatively low levels. For example, the
numerical value of the normalized leakage current of a capacitor of
the present invention is, in some embodiments, less than about 1
.mu.A/.mu.F*V, in some embodiments less than about 0.5
.mu.A/.mu.F*V, and in some embodiments, less than about 0.1
.mu.A/.mu.F*V, where .mu.A is microamps and uF*V is the product of
the capacitance and the rated voltage.
The electrical properties, such as described above, may even be
maintained after aging for a substantial amount of time at high
temperatures. For example, the values may be maintained for about
100 hours or more, in some embodiments from about 300 hours to
about 3000 hours, and in some embodiments, from about 400 hours to
about 2500 hours (e.g., 500 hours, 600 hours, 700 hours, 800 hours,
900 hours, 1000 hours, 1100 hours, 1200 hours, or 2000 hours) at
temperatures ranging from about 100.degree. C. to about 250.degree.
C., and, in some embodiments from about 100.degree. C. to about
225.degree. C., and in some embodiments, from about 100.degree. C.
to about 225.degree. C. (e.g., 100.degree. C., 125.degree. C.,
150.degree. C., 175.degree. C., or 200.degree. C.).
The present invention may be better understood by reference to the
following examples.
Test Procedures
Equivalent Series Resistance (ESR)
Equivalence series resistance may be measured using a Keithley 3330
Precision LCZ meter with Kelvin Leads 2.2 volt DC bias and a 0.5
volt peak to peak sinusoidal signal. The operating frequency was
100 kHz and the temperature was 23.degree. C..+-.2.degree. C.
Capacitance
The capacitance was measured using a Keithley 3330 Precision LCZ
meter with Kelvin Leads with 2.2 volt DC bias and a 0.5 volt peak
to peak sinusoidal signal. The operating frequency was 120 Hz and
the temperature was 23.degree. C..+-.2.degree. C.
Fine Leaks Testing:
Assembled parts in appropriate hermetically sealed housing were put
into a helium chamber (4.3 kg/cm). After 1 hour, the assembled
parts were measured with a helium mass detector (Pfeiffer
Vacuum--HLT560) with a rejection limit of 10.sup.-8
ccatms.sup.-1.
Example 1
A tantalum anode (5.20 mm.times.3.70 mm.times.0.85 mm) was anodized
at 125V in a liquid electrolyte to 10 .mu.F. A conductive polymer
coating was then formed by dipping the entire anode into a
poly(3,4-ethylenedioxythiophene) ("PEDT") dispersion (Clevios.TM.
K, solids content of 1.1%). The part was then dried at 125.degree.
C. for 20 minutes. This process was repeated 10 times. Thereafter,
the part was dipped at a speed of 0.1 mm/s into a PEDT dispersion
(solids content of 2.8%) so that the dispersion reached the
shoulder of the part. The part was left in the dispersion for 10
seconds, dried at 125.degree. C. for 30 minutes, and then cooled
down to room temperature. This process was repeated 5 times. The
part was then coated with graphite and silver. A copper-based
leadframe material was used to finish the assembly process. A
single cathode connective member was attached to the lower surface
of the capacitor element using a silver adhesive. The tantalum wire
of the capacitor element was then laser welded to an anode
connective member.
The anode and cathode connective members of the leadframe were then
glued to a gold cathode termination and welded to a gold anode
termination located inside a ceramic housing having a length of
11.00 mm, a width of 6.00 mm, and a thickness of 2.20 mm. The
housing had gold plated solder pads on the bottom inside part of
ceramic housing. The adhesive employed for the cathode connection
was a tin solder paste (EPO-Tek E3035) and the adhesive was applied
only between the leadframe portions and gold plated solder pad. The
welding employed for the anode connection was a resistance welding
and the energy of 190 W was applied between the leadframe portions
and ceramic housing gold plated solder pad during 90 ms. The
assembly was then loaded in a convection reflow oven to solder the
paste. After that, a Kovar.RTM. lid having a length of 9.95 mm, a
width of 4.95 mm, and a thickness of 0.10 mm was placed over the
top of the container, closely on the seal ring of the ceramic
housing (Kovar.RTM. ring having a thickness of 0.30 mm) so that
there was no direct contact between the interior surface of the lid
and the exterior surface of the attached capacitor. The resulting
assembly was placed into a welding chamber and purged with nitrogen
gas for 120 minutes before seam welding between the seal ring and
the lid was performed. No additional burn-in or healing was
performed after the seam welding. Multiple parts (50) were made in
this manner.
Example 2
A capacitor element was initially formed and connected to anode and
cathode connective members as described in Example 1. The anode and
cathode connective members were then resistance welded to stainless
steel portions of a termination located on a lower wall as shown in
FIG. 3. The welding occurred at an energy of 190 W for 90 ms. A
metal lid containing lips as shown in FIG. 3 was then placed over
the wall to form a housing having a length of 20.10 mm, a width of
12.50 mm, and a thickness of 4.60 mm. Stainless steel pads
(isolated through the glass bushing from the part of metal housing)
were located between the contact areas of the lid and the bottom
wall. The resulting assembly was placed into a welding chamber and
purged with nitrogen gas for 120 minutes before seam welding. No
additional burn-in or healing was performed after the seam welding.
Multiple parts (50) were made in this manner.
The finished capacitors of Examples 1 and 2 were tested for fine
leaks as described above. It was determined that more than 95% of
the parts of Example 2 were determined to pass the mass detection
limit, as compared to only 81% of the parts of Example 1. It is
believed that the high yield was due to using of the lip design for
the lid, which enabled a more stable connection between the
components of housing and better performance for seam welding
process. The finished capacitors of Examples 1-2 were also tested
for electrical performance (i.e., leakage current, ESR, and
capacitance) by attaching the parts via solder paste to a PCB
board. The measurements were conducted at 25.degree. C. and then
repeated after 2000 hours of storage at a temperature of
125.degree. C. and an applied rated voltage of 35V. The results are
set forth below.
TABLE-US-00001 Electrical Performance Electrical Performance after
at 25.degree. C. 2000 hours, 125.degree. C./35 V ESR Cap ESR Cap
Sample DCL [.mu.A] [mOhm] [.mu.F] DCL [.mu.A] [mOhm] [.mu.F]
Example 1 0.05 122 8.58 0.25 133 8.44 Example 2 0.58 126 8.24 1.47
104 8.12
These and other modifications and variations of the present
invention may be practiced by those of ordinary skill in the art,
without departing from the spirit and scope of the present
invention. In addition, it should be understood that aspects of the
various embodiments may be interchanged both in whole or in part.
Furthermore, those of ordinary skill in the art will appreciate
that the foregoing description is by way of example only, and is
not intended to limit the invention so further described in such
appended claims.
* * * * *